Biomedical subjects

Daniel L Schacter

Publications and source records attributed to Daniel L Schacter.

At least 37 records · Page 2Linked to original sources

PubMed2005

Hippocampal and neocortical activation during repetitive encoding in older persons.

Episodic memory function is known to decline in the course of normal aging; however, compensatory techniques can improve performance significantly in older persons. We investigated the effects of the memory enhancing technique of repetition encoding on brain activation using event-related functional magnetic resonance imaging (fMRI). Twelve healthy older adults without cognitive impairment were studied with fMRI during repetitive encoding of face-name pairs. During the first encoding trials of face-name pairs that were subsequently remembered correctly, activation of the hippocampus and multiple neocortical regions, including prefrontal, parietal and fusiform cortices, was observed. The second and third encoding trials resulted in continued activation in neocortical regions, but no task-related response within the hippocampus. Functional imaging of successful memory processes thus permits us to detect regionally specific responses in the aging brain. Our findings suggest that hippocampal function is preserved in normal aging and that repetition-based memory enhancing techniques may engage primarily neocortical attentional networks.

Age Factors↗

PubMed2005

Emotional content and reality-monitoring ability: fMRI evidence for the influences of encoding processes.

Memory for emotional items can be less prone to some types of memory distortion, such as reality-monitoring errors, than memory for neutral items. The present fMRI study examined whether this enhanced reality-monitoring accuracy reflects engagement of distinct processes recruited during encoding of emotional information. Participants only imagined named objects (word-only trials) or imagined named objects and then also viewed photos of them (word-picture trials). Half of the items were emotional (e.g., snake, casket). Later, participants heard object names and indicated whether the corresponding photo had been shown. Reality-monitoring errors occurred when participants attributed an item from a word-only trial to a word-picture trial. Such misattribution errors occurred less frequently for emotional than neutral items. Activity in emotion-processing regions (e.g., orbitofrontal cortex, amygdala) reduced the likelihood of later misattributions, likely due in part to interactions with regions that promote memory accuracy (e.g., the hippocampus). Distinct neural processes also increased the likelihood of reality-monitoring errors, depending on the emotional content of the items. Activity spanning the fusiform and parahippocampal gyri (likely reflecting mental imagery) increased the likelihood of reality-monitoring errors for neutral items, while activity in the anterior cingulate increased the likelihood of reality-monitoring errors for emotional items.

Adolescent↗

PubMed2005

Patients with mild Alzheimer's disease attribute conceptual fluency to prior experience.

Patients with Alzheimer's disease (AD) have been found to be relatively dependent on familiarity in their recognition memory judgments. Conceptual fluency has been argued to be an important basis of familiarity. This study investigated the extent to which patients with mild AD use conceptual fluency cues in their recognition decisions. While no evidence of recognition memory was found in the patients with AD, enhanced conceptual fluency was associated with a higher rate of "Old" responses (items endorsed as having been studied) compared to when fluency was not enhanced. The magnitude of this effect was similar for patients with AD and healthy control participants. Additionally, ERP recordings time-locked to test item presentation revealed preserved modulations thought critical to the effect of conceptual fluency on test performance (N400 and late frontal components) in the patients with AD, consistent with the behavioral results. These findings suggest that patients with mild AD are able to use conceptual fluency in their recognition judgments and the neural mechanisms supporting such processing is maintained.

Aged↗

PubMed2005

The case of K.C.: contributions of a memory-impaired person to memory theory.

K.C. has been investigated extensively over some 20 years since a motorcycle accident left him with widespread brain damage that includes large bilateral hippocampal lesions, which caused a remarkable case of memory impairment. On standard testing, K.C.'s anterograde amnesia is as severe as that of any other case reported in the literature, including H.M. However, his ability to make use of knowledge and experiences from the time before his accident shows a sharp dissociation between semantic and episodic memory. A good deal of his general knowledge of the world, including knowledge about himself, is preserved, but he is incapable of recollecting any personally experienced events. In displaying such "episodic amnesia," which encompasses an entire lifetime of personal experiences, K.C. differs from many other amnesic cases. Here, we document for the first time the full extent of K.C.'s brain damage using MRI-based quantitative measurements. We then review the many investigations with K.C. that have contributed to our understanding not only of episodic and semantic memory but also to the development of other aspects of memory theory. These include the distinction between implicit and explicit memory, the prospect of new learning in amnesia, and the fate of recent and remote memory for autobiographical and public events, people, and spatial locations.

Adult↗

PubMed2005

Metacognition and false recognition in patients with frontal lobe lesions: the distinctiveness heuristic.

The distinctiveness heuristic is a response mode in which participants expect to remember vivid details of an experience and make recognition decisions based on this metacognitive expectation. Whereas much is known about the cognitive processes that are involved in using the distinctiveness heuristic, little is known about the corresponding brain processes. Because such metacognitive processes that involve the evaluation and control of one's memory are believed to be dependent upon the frontal lobes, the authors examined whether the distinctiveness heuristic could be engaged to reduce false recognition in a repetition lag paradigm in patients with lesions of their frontal lobes. Half of the participants studied pictures and corresponding auditory words; the other half studied visual and auditory words. Studied and novel items were presented at test as words only, with all novel items repeating after varying lags. Controls who studied pictures were able to reduce their false recognition of repeated lag items relative to those controls who studied words, demonstrating their use of the distinctiveness heuristic. Patients with frontal lobe lesions showed similar levels of false recognition regardless of whether they studied pictures and words or words only, suggesting that they were unable to use the distinctiveness heuristic. The authors suggest that the distinctiveness heuristic is a metacognitive strategy, dependent upon the frontal lobes, that may be engaged by healthy individuals to reduce their false recognition.

Adult↗

PubMed2005

Metacognition and false recognition in Alzheimer's disease: further exploration of the distinctiveness heuristic.

The distinctiveness heuristic is a response mode in which participants expect to remember vivid details of an experience and make recognition decisions on the basis of this metacognitive expectation. The authors examined whether the distinctiveness heuristic could be engaged to reduce false recognition in a repetition-lag paradigm in patients with Alzheimer's disease (AD). Patients with AD were able to use the distinctiveness heuristic--though not selectively--and thus they showed reduction of both true and false recognition. The authors suggest that patients with AD can engage in decision strategies on the basis of the metacognitive expectation associated with use of the distinctiveness heuristic, but the patients' episodic memory impairment limits both the scope and effectiveness of such strategies.

Aged↗

PubMed2005

Failing to get the gist: reduced false recognition of semantic associates in semantic dementia.

In 2 experiments involving patients with semantic dementia, the authors investigated the impact of semantic memory loss on both true and false recognition. Experiment 1 involved recognition memory for categories of everyday objects that shared a predominantly semantic relationship. The patients showed preserved item-specific recollection for the pictorial stimuli but, compared with control participants, exhibited significantly reduced utilization of gist information regarding the categories of objects. The latter result is consistent with the patients' degraded semantic knowledge. Experiment 2 involved categories of abstract objects that were related to one another perceptually rather than semantically. Patients with semantic dementia obtained item-specific recollection and gist memory scores that were indistinguishable from those of control participants. These results suggest that the reduction in gist memory in semantic dementia is largely specific to semantic representations and cannot be attributed to general difficulty with abstracting and/or utilizing gistlike commonalities between stimuli.

Aged↗

PubMed2005

Comparing source-based and gist-based false recognition in aging and Alzheimer's disease.

This study examined 2 factors contributing to false recognition of semantic associates: errors based on confusion of source and errors based on general similarity information or gist. The authors investigated these errors in patients with Alzheimer's disease (AD), age-matched control participants, and younger adults, focusing on each group's ability to use recollection of source information to suppress false recognition. The authors used a paradigm consisting of both deep and shallow incidental encoding tasks, followed by study of a series of categorized lists in which several typical exemplars were omitted. Results showed that healthy older adults were able to use recollection from the deep processing task to some extent but less than that used by younger adults. In contrast, false recognition in AD patients actually increased following the deep processing task, suggesting that they were unable to use recollection to oppose familiarity arising from incidental presentation.

Adolescent↗

PubMed2005

Impaired implicit memory for gist information in amnesia.

In 2 experiments using a converging associates paradigm, the authors evaluated implicit memory for gist information in amnesic patients. In Experiment 1, participants saw multiple sets of associates, each converging on a nonpresented theme word, and were then tested using an implicit word stem completion test and an explicit cued recall test. Amnesic patients showed intact implicit and impaired explicit memory for studied words, but memory for nonpresented lures was impaired, regardless of retrieval instructions. To evaluate whether impaired implicit memory for lures was due to accelerated forgetting of gist information, short study lists were used in Experiment 2, each consisting of a single set of associates. Amnesics' implicit memory for lures was again impaired. These results point to an inability to encode robust gist representations as the cause of impaired gist memory in amnesia.

Aged↗

PubMed2005

fMRI evidence for the role of recollection in suppressing misattribution errors: the illusory truth effect.

Misattribution refers to the act of attributing a memory or idea to an incorrect source, such as successfully remembering a bit of information but linking it to an inappropriate person or time [Jacoby, L. L., Kelley, C., Brown, J., & Jasechko, J. (1989). Becoming famous overnight: Limits on the ability to avoid unconscious influences of the past. Journal of Personality and Social Psychology, 56, 326-338; Schacter, D. L. (1999). The seven sins of memory: Insights from psychology and cognitive neuroscience. American Psychologist, 54, 182-203; Schacter, D. L. (2001). The seven sins of memory: How the mind forgets and remembers. Boston: Houghton Mifflin]. Cognitive studies have suggested that misattribution errors may occur in the absence of recollection for the details of an initial encounter with a stimulus, but little is known about the neural basis of this memory phenomenon. Here we used functional magnetic resonance imaging (fMRI) to examine the hypothesized role of recollection in counteracting the illusory truth effect, a misattribution error whereby perceivers systematically overrate the truth of previously presented information. Imaging was conducted during the encoding and subsequent judgment of unfamiliar statements that were presented as true or false. Event-related fMRI analyses were conditionalized as a function of subsequent performance. Results demonstrated that encoding activation in regions previously associated with successful recollection--including the hippocampus and the ventrolateral prefrontal cortex (PFC)--correlated with the successful avoidance of misattribution errors, providing initial neuroimaging support for earlier cognitive accounts of misattribution.

Acoustic Stimulation↗

PubMed2005

Electrophysiological dissociation of picture versus word encoding: the distinctiveness heuristic as a retrieval orientation.

Event-related potentials (ERPs) were used to investigate the neural processes underlying the distinctiveness heuristic-a response mode in which participants expect to remember vivid details of an experience and make recognition decisions based on this metacognitive expectation. One group of participants studied pictures and auditory words; another group studied visual and auditory words. Studied and novel items were presented at test as words only, with all novel items repeating after varying lags. ERP differences were seen between the word and picture groups for both studied and novel items. For the novel items, ERP differences were largest in frontal and central midline electrodes. In separate analyses, the picture group showed the greatest ERP differences between item types in a parietally based component from 550 to 1000 msec, whereas the word group showed the greatest differences in a frontally based component from 1000 to 2000 msec. The authors suggest that the distinctiveness heuristic is a retrieval orientation that facilitates reliance upon recollection to differentiate between item types. Although the picture group can use this heuristic and its retrieval orientation on the basis of recollection, the word group must engage additional postretrieval processes to distinguish between item types, reflecting the use of a different retrieval orientation.

Adult↗

PubMed2005

The modality effect in false recognition: evidence for test-based monitoring.

False recognition in the Deese/Roediger-McDermott (DRM) paradigm has been shown to be greater following auditory study than following visual study, but there are competing explanations for this effect. We generalized this phenomenon in Experiment 1, finding an equivalent modality effect for associative (DRM) lists and categorized lists. Because conscious generationand subsequent monitoring of related lures during study is infrequent for categorized lists, this result is inconsistent with the idea that the modality effect is due to a study-based monitoring process. An alternative explanation is that visual study impairs relational processing relative to auditory study, which could cause a modality effect by lowering false recognition of related lures. We tested this idea in Experiment 2, by switching to a meaning-based test that is sensitive only to the retrieval of relational information. A modality effect was not obtained for either type of list on this test. The results from both experiments were predicted by a test-based monitoring account, rather than by the study-based monitoring or relational processing accounts.

Attention↗

PubMed2004

Graded recall success: an event-related fMRI comparison of tip of the tongue and feeling of knowing.

Insights into memory retrieval processes can be obtained by examining graded recall success, specifically, tip-of-the-tongue (TOT) and feeling-of-knowing (FOK) states. TOT is defined as a recall failure accompanied by a strong feeling of imminent retrieval, and FOK as a recall failure accompanied by a feeling of future ability to recognize the item. The present fMRI study examined the brain regions associated with both intermediate retrieval states in a within-subject, within-memory system design. Subjects were presented with general knowledge questions and were instructed to respond to each with one of four options: Know, indicating successful retrieval of the answer; TOT; FOK; or Don't know, indicating retrieval failure. Different patterns of activation in several brain regions including prefrontal cortex were associated with TOT and FOK states. For example, TOT was associated with activation in anterior cingulate, right dorsal and inferior, and bilateral anterior, prefrontal cortex. TOT and FOK elicited similar levels of activation in parietal regions, both significantly greater than that associated with Know and Don't know responses. The results are interpreted in the light of theories of the role of prefrontal cortex in recall and cognitive conflict.

Adolescent↗

PubMed2004

The neural origins of specific and general memory: the role of the fusiform cortex.

Recognition of an object can be based on memory for specific details of a prior encounter with the object, or on a more general memory for the type of object previously encountered. Responding on the basis of general information alone can sometimes produce memory errors involving both distortion and forgetting, but little is known about the neural origins of general versus specific recognition. We extended the standard subsequent memory paradigm to examine whether neural activity at encoding predicts whether an object will subsequently elicit specific as compared to general memory. During event-related functional magnetic resonance imaging (fMRI), participants viewed objects and made size judgments about them. Later, they viewed same, similar, and new objects, labeling each as "same," "similar," or "new." Specific recognition was indicated by a "same" response to a same object. By contrast, general, non-specific recognition was indicated by either a "same" response to a similar object (false memory) or a "similar" response to a same object (partial memory). As predicted, specific recognition, as compared to non-specific recognition, was associated with encoding-related activity in the right fusiform cortex, while non-specific recognition, as compared to forgetting, was associated with encoding-related activity in the left fusiform cortex. Furthermore, all successful recognition (specific and general), as compared to forgetting, was associated with encoding-related activity in bilateral fusiform cortex. These results suggest that the right fusiform cortex is associated with specific feature encoding, while the left fusiform cortex is involved in more general object encoding.

Adult↗

PubMed2004

An electrophysiological investigation of the relationship between conceptual fluency and familiarity.

Brain potentials associated with the manipulation of conceptual fluency in a recognition memory paradigm were recorded. Enhanced fluency was associated with attenuation of the N400 and an increased rate of subjects' endorsing both studied and non-studied items as having been studied ("old" responses) in the recognition test. Differences were also found in latencies previously associated with post-retrieval processing, such that in the setting of enhanced fluency (1) non-studied items were associated with a positive wave from 800 to 1600 ms and (2) items endorsed as "new" were more positive than those endorsed as "old" from 1200 to 1600 ms. The effects on the N400 may be related to the impact of fluency on familiarity, whereas later processing may be involved in the attribution of fluency to prior experience.

Adolescent↗

PubMed2004

The cognitive neuroscience of memory distortion.

Memory distortion occurs in the laboratory and in everyday life. This article focuses on false recognition, a common type of memory distortion in which individuals incorrectly claim to have encountered a novel object or event. By considering evidence from neuropsychology, neuroimaging, and electrophysiology, we address three questions. (1) Are there patterns of neural activity that can distinguish between true and false recognition? (2) Which brain regions contribute to false recognition? (3) Which brain regions play a role in monitoring or reducing false recognition? Neuroimaging and electrophysiological studies suggest that sensory activity is greater for true recognition compared to false recognition. Neuropsychological and neuroimaging results indicate that the hippocampus and several cortical regions contribute to false recognition. Evidence from neuropsychology, neuroimaging, and electrophysiology implicates the prefrontal cortex in retrieval monitoring that can limit the rate of false recognition.

Animals↗

PubMed2004

A sensory signature that distinguishes true from false memories.

Human behavioral studies show that there is greater sensory/perceptual detail associated with true memories than false memories. We therefore hypothesized that true recognition of abstract shapes would elicit greater visual cortical activation than would false recognition. During functional magnetic resonance imaging (fMRI), participants studied exemplar shapes and later made recognition memory decisions ("old" or "new") concerning studied exemplars (old shapes), nonstudied lures (related shapes) and new shapes. Within visual processing regions, direct contrasts between true recognition ("old" response to an old shape; old-hit) and false recognition ("old" response to a related shape; related-false alarm) revealed preferential true recognition-related activity in early visual processing regions (Brodmann area (BA)17, BA18). By comparison, both true and false recognition were associated with activity in early and late (BA19, BA37) visual processing regions, the late regions potentially supporting "old" responses, independent of accuracy. Further analyses suggested that the differential early visual processing activity reflected repetition priming, a type of implicit memory. Thus, the sensory signature that distinguishes true from false recognition may not be accessible to conscious awareness.

Adult↗

PubMed2004

Cortical activity reductions during repetition priming can result from rapid response learning.

Recent observation of objects speeds up their subsequent identification and classification. This common form of learning, known as repetition priming, can operate in the absence of explicit memory for earlier experiences, and functional neuroimaging has shown that object classification improved in this way is accompanied by 'neural priming' (reduced neural activity) in prefrontal, fusiform and other cortical regions. These observations have led to suggestions that cortical representations of items undergo 'tuning', whereby neurons encoding irrelevant information respond less as a given object is observed repeatedly, thereby facilitating future availability of pertinent object knowledge. Here we provide experimental support for an alternative hypothesis, in which reduced cortical activity occurs because subjects rapidly learn their previous responses. After a primed object classification (such as 'bigger than a shoebox'), cue reversal ('smaller than a shoebox') greatly slowed performance and completely eliminated neural priming in fusiform cortex, which suggests that these cortical item representations were no more available for primed objects than they were for new objects. In contrast, prefrontal cortex activity tracked behavioural priming and predicted the degree to which cue reversal would slow down object classification--highlighting the role of the prefrontal cortex in executive control.

Adolescent↗